1. Field of the Invention
An aspect of the present invention relates to an optical pickup for an optical recording and/or reproducing apparatus used for recording and/or reproducing information to/from an optical recording medium.
More particularly, an aspect of the present invention relates to an optical pickup for an optical recording and/or reproducing apparatus capable of recording and/or reproducing information from/to various types of optical recording media of different densities, and improving capability to cope with an optical recording medium, which is tilted.
2. Description of the Related Art
An optical pickup of an optical recording and/or reproducing apparatus capable of recording information on an optical disc, which is an optical recording medium, includes an optical pickup for moving along a direction of a radius of the disc, to irradiate light on a recording surface of the disc and receive the light reflected therefrom. The optical pickup has an actuator to help an object lens maintain a predetermined position and posture with respect to the recording surface of the disc.
FIG. 1 illustrates an optical pickup actuator disclosed in Korean Patent Publication No. 2003-69459. Referring FIG. 1, the optical pickup actuator includes a holder 11 fixed at a base 10, a blade 13 holding the object lens 12, a plurality of elastic supports 14a, 14b, and a magnetic driving portion for moving the blade 13 in a focusing (F) or tracking direction (T).
The magnetic driving portion has a pair of magnets 15 disposed around the blade 13, an inner yoke 16 and an outer yoke 17 both installed at the base 10, and a focusing coil 18 and a tracking coil 19 both wrapped on the blade 13.
The elastic support 14a is located along an inner circumference with respect to a radial direction of a disc (D) and the elastic support 14b in located along an outer circumference with respect to a radial direction of the disc (D). The outer elastic support 14b is longer, and has relatively less rigidity than the inner elastic support 14a.
In the above structured actuator, in order to trace a focusing position by a deflection of the disc upon optical recording and/or reproducing, rolling is performed in a focusing direction of the blade 13. The support 14b has less rigidity and more flexibility than the support 14a, accordingly permitting more rolling inside than outside.
As illustrated in FIG. 2A, in a case that the disc (D) is tilted upward from an outer circumferential direction, the blade ascends and rolling is performed in a (+) direction. Accordingly, the object lens 12 performs focusing on the recording surface of the disc, by tracing the tilted disc in a focusing direction.
As illustrated in FIG. 2B, in a case that the disc (D) is tilted downward from an outer circumferential direction, the blade descends and rolling is performed in a (−) direction. Accordingly, when recording and/or reproducing information on the disc (D) tilted downward, the blade 13 descends and performs rolling in a (−) direction, to change postures, such that focusing is exactly performed on the recording surface of the disc (D).
In order to cope with a tilted disc, a gradient changes according to positional changes of the blade 13 in a focusing direction. This gradient change is achieved using the elastic displacement differences of the outer and inner elastic supports 14a, 14b.
There are many different optical discs on the market including CD (Compact Disk), DVD (Digital Versatile Disk), BD-DVD (High-Definition DVD), and BD (Blue Laser Disk). Accordingly, there are active developments for an optical pickup capable of being used with various types of optical discs having different recording densities. In such a compatible optical pickup, more than one object lens can be employed and the employed object lens varies a focusing distance, that is, a WD (Working Distance) varies between optical discs having different recording densities.
As mentioned above, each of the optical discs has a different WD (Working Distance), and therefore, the blade is controlled to be driven in a focusing direction, to maintain a WD (Working Distance) with any optical disc employed.
As illustrated in FIGS. 1 or 2B, if the blade 13 is structured to have rolling in order to cope with the tilted disc, regardless of a deflection degree of the disc, a focusing error may occur.